Direct selective synthesis of para-xylene by reacting an aromatic compound with a methylating agent formed from CO, Co2 and H2

ABSTRACT

It has been discovered that para-xylene (PX) can be synthesized with improved selectivity by reacting an aromatic compound such as toluene and/or benzene with a reactant(s) such as a combination of hydrogen and carbon monoxide and/or carbon dioxide and/or methanol or methylating agents produced therefrom. Catalytic reaction systems are employed, such as crystalline or amorphous aluminosilicates having one-dimensional channel structure, para-alkyl selectivated crystalline or amorphous aluminosilicates, para-alkyl selectivated substituted aluminosilicates, crystalline or amorphous substituted silicates having one-dimensional channel structure, para-alkyl selectivated substituted silicates, crystalline or amorphous aluminophosphates, para-alkyl selectivated crystalline or amorphous aluminophosphates, para-alkyl selectivated zeolite-bound zeolite and para-alkyl selectivated substituted aluminophosphates, and mixtures thereof. The catalytic reaction systems may be selectivated with organometallic compounds, compounds of elements selected from Groups 1 through 16, coke, and mixtures thereof. Using this process, catalyst stability and life is improved.

FIELD OF THE INVENTION

The present invention relates to methods for synthesis of xylenes bycatalytic methylation of toluene and benzene, and more particularlyrelates, in one embodiment, to methods for synthesis of direct,selective synthesis of para-xylene by catalytic methylation of tolueneand benzene.

BACKGROUND OF THE INVENTION

Of the xylene isomers, i.e., ortho-, meta-, and para-xylene, thepara-xylene (PX) is of particular value as a large volume chemicalintermediate in a number of applications being useful in the manufactureof terephthalates which are intermediates for the manufacture of PET.One source of feedstocks for manufacturing PX is by disproportionationof toluene into xylenes. One of the disadvantages of this process isthat large quantities of benzene are also produced. Another source offeedstocks used to obtain PX involves the isomerization of a feedstreamthat contains non-equilibrium quantities of mixed ortho- and meta-xyleneisomers (OX and MX, respectively) and is lean with respect to PXcontent. A disadvantage of this process is that the separation of the PXfrom the other isomers is expensive.

Zeolites are known to catalyze the reaction of toluene with otherreactants to make xylenes. Some zeolites are silicate-based materialswhich are comprised of a silica lattice and, optionally, aluminacombined with exchangeable cations such as alkali or alkaline earthmetal ions. Although the term “zeolites” includes materials containingsilica and optionally alumina, it is recognized that the silica andalumina portions may be replaced in whole or in part with other oxides.For example, germanium oxide, tin oxide, phosphorus oxide, and mixturesthereof can replace the silica portion. Boron oxide, iron oxide, galliumoxide, indium oxide, and mixtures thereof can replace the aluminaportion. Accordingly, the terms “zeolite”, “zeolites” and “zeolitematerials”, as used herein, shall mean not only materials containingsilicon and, optionally, aluminum atoms in the crystalline latticestructure thereof, but also materials which contain suitable replacementatoms for such silicon and aluminum, such as gallosilicates,borosilicates, ferrosilicates, and the like.

The term “zeolite, “zeolites”, and “zeolite materials” as used herein,besides encompassing the materials discussed above, shall also includealuminophosphate-based materials. Aluminophosphate zeolites are made ofalternating AlO₄ and PO₄ tetrahedra. Aluminophosphate-based materialshave lower acidity compared to aluminosilicates. The lower acidityeliminates many side reactions, raises reactants' utilization, andextends catalyst life. Aluminophosphate-based zeolites are oftenabbreviated as ALPO. Substitution of silicon for P and/or a P—Al pairproduces silicoaluminophosphate zeolites, abbreviated as SAPO.

Processes have been proposed for the production of xylenes by themethylation of toluene using a zeolite catalyst. For instance, U.S. Pat.No. 3,965,207 involves the methylation of toluene with methanol using azeolite catalyst such as a ZSM-5. U.S. Pat. No. 4,670,616 involves theproduction of xylenes by the methylation of toluene with methanol usinga borosilicate zeolite which is bound by a binder such as alumina,silica, or alumina-silica. One of the disadvantages of such processes isthat catalysts deactivate rapidly due to build up of coke and heavyby-products. Another disadvantage is that methanol selectivity topara-xylene, the desirable product, has been low, in the range of 50 to60%. The balance is wasted on the production of coke and otherundesirable compounds.

It has been further demonstrated that alkylaromatic compounds can besynthesized by reacting an aromatic compound such as toluene with amixture of carbon monoxide (CO), carbon dioxide (CO₂), and hydrogen (H₂)(synthesis gas) at alkylation conditions in the presence of a catalystsystem, which comprises (1) a composite of oxides of zinc, copper,chromium, and/or cadmium; and (2) an aluminosilicate material, eithercrystalline or amorphous, such as zeolites or clays; as disclosed inU.S. Pat. Nos. 4,487,984 and 4,665,238. Such catalyst systems, however,are not capable of producing greater than equilibrium concentrations ofpara-xylene (PX) in the xylene-fraction product. Typically, thexylene-fraction product contains a mixture of xylene isomers at or nearthe equilibrium concentration, i.e., 24% PX, 54% MX, and 22% OX. Thelack of para-xylene selectivity in alkylation of toluene with syngas canbe caused by (1) the acidic sites on the surface outside the zeolitechannels, and/or (2) the channel structure not being able todifferentiate para-xylene from its isomers. It would be desirable forthe toluene alkylation to be more para-alkyl selective due to the muchhigher value of PX compared to that of MX and OX. Furthermore, suchprocesses suffer from catalyst deactivation as well. In addition, theprior art disclosed neither syngas alkylation to alkyl aromaticcompounds nor syngas selective alkylation to high purity PX usingalumino-phosphate-based materials.

It has been recognized that certain zeolites can be modified to enhancetheir molecular-sieving or shape-selective capability. Such modificationtreatments are usually called “zeolite selectivation.” Selectivatedzeolites can more accurately differentiate molecules on the basis ofmolecular dimension or steric characteristics than the unselectivatedprecursors. For example, silanized ZSM-5 zeolites adsorbed PX much morepreferentially over MX than untreated ZSM-5. It is believed that thedeposition of silicon oxide onto zeolite surfaces from the silanizationtreatment has (1) passivated the active sites on the external surface ofzeolite crystals, and (2) narrowed zeolitic pores to facilitate thepassage of the smaller PX molecules and prevent the bigger MX and OXmolecules from entering or exiting from the pores. In this application,the term “para-alkyl selectivation” refers to modifying a catalyst orcatalytic reaction system so that it preferentially forms more PX thanthe expected equilibrium proportions relative to the other isomers.

Zeolite selectivation can be accomplished using many techniques. Reportsof using compounds of silicon, phosphorous, boron, antimony, coke,magnesium, etc. for selectivation have been documented. Unfortunatelymany, if not most of the zeolites used in the prior art have undesirablyshort active lifetimes before they deactivate and have to be reactivatedor replaced.

There remains a need for still further improved processes for catalyticPX synthesis which minimizes or avoids the disadvantages of priorsystems, which include low PX selectivity, low methanol selectivity,rapid catalyst deactivation, and the like.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod in which PX of high product concentration is synthesized viaalkylation of toluene and/or benzene with a mixture including H₂, and COand/or CO₂ and/or methanol in a catalytic reaction system.

It is another object of the present invention to provide a method forproducing PX in greater than equilibrium product concentration, e.g.greater than 30%, in the xylene product fraction as compared to prior,equilibrium concentrations of about 24%.

Still another object of the invention is to provide a method for thedirect, selective production of PX from toluene and/or benzene which hasa high aromatic conversion, e.g. at least above 5%, preferably above15%, most preferably as high as possible.

In carrying out these and other objects of the invention, there isprovided, in one form, a method for forming para-xylene (PX) involvingreacting a feed containing an aromatic compound of toluene, benzene andmixtures thereof with a methylating agent formed from H₂, and CO and/orCO₂ and/or methanol and mixtures thereof, in the presence of a catalyticreaction system which converts at least 5% of the aromatic compound to amixture of xylenes, where PX comprises at least 30% of the mixture ofxylenes.

It should be stressed that the invention provides a process forincreased selectivity to para-xylene. Further, the invention employsaluminophosphate-based catalysts for selective para-xylene synthesis,whether or not the aluminophosphate-based materials are para-alkylselectivated. Additionally, the invention prolongs catalyst lifetime byreducing, even eliminating catalyst deactivation, as compared with priorPX forming processes. Another advantage of the invention is thesimultaneous cracking of paraffins and olefins present while processingunextracted toluene, or unextracted mixtures of toluene and benzene.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process to synthesize PX withpara-alkyl selective alkylation of toluene and/or benzene with a mixturecontaining, as predominant components thereof, hydrogen, carbonmonoxide, and/or carbon dioxide and/or methanol in the presence of acatalyst system. A method has been discovered by which the productselectivity to para-xylene for an aromatic alkylation process using asalkylating agents mixtures of H₂, CO, and/or CO₂ and/or methanol issignificantly enhanced. The improvement in para-xylene selectivity isachieved by treating the molecular sieve zeolite materials with properchemical compounds to (1) inhibit the external acidic sites to minimizearomatic alkylation on the non-para positions, and/or the isomerizationof the para-alkylated compounds, and/or (2) impose more restrictions onthe channel structure to facilitate the formation and transport ofpara-alkylated aromatic compounds, in one non-limiting explanation ofthe mechanism of the invention. It must be understood that suchtreatment may be performed on aluminophosphate catalyst reaction systemsof this invention, but that some aluminophosphate catalyst reactionsystems do not require this para-alkyl selectivation treatment to beeffective at para-alkyl selectivation in the methods of this invention.

The catalytic reaction systems suitable for this invention include (1) afirst component of one or more than one of the metals or oxides of themetal elements selected from Groups 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,12, 13, 14, 15 and 16 (new IUPAC notation, e.g. zinc, copper, chromium,cadmium, palladium, ruthenium, manganese, etc.), and (2) a secondcomponent of one or more than one of the zeolite or amorphous materials,some of which are selectivated for para-position selectivity. The firstand second components may be chemically mixed, physically mixed, andcombinations thereof, as will be described.

One type of the zeolite materials would be silicate-based zeolites suchas faujasites, mordenites, pentasils, etc.

Zeolite materials suitable for this invention include silicate-basedzeolites and amorphous compounds. Silicate-based zeolites are made ofalternating SiO₂ and MO_(x) tetrahedra, where in the formula M is anelement selected from the Groups 1 through 16 of the Periodic Table (newIUPAC). These types of zeolites have 8-, 10-, or 12-membered oxygen ringchannels. Silicate-based materials are generally acidic. The morepreferred zeolites of this invention include 10- and 12-membered ringzeolites, such as ZSM-5, ZSM-11, ZSM-22, ZSM-48, ZSM-57, etc.

One of the disadvantages to the use of many unselectivatedsilicate-based materials for such PX synthesis systems is the lack ofproduct selectivity (i.e. an undesirably broad product distributionresults). The acidity and structure of many silicate-based materials aresuch that they often promote many undesirable side reactions (e.g.dealkylation, isomerization, multi-alkylation, oligomerization, andcondensation) which deactivate the catalysts and lower the productvalue. It follows that, silicate-based materials are typically notcapable of delivering the shape selectivity for increasing the yield forhigh-value products such as para-xylene (PX).

Some of the silicate-based materials have one-dimensional channelstructures, which are capable of generating higher-than-equilibrium PXselectivity. These materials may optionally be para-alkyl selectivated.Other silicate-based materials having two- or three-dimensional channelstructures are preferably para-alkyl selectivated or modified to be moreselective through the use of certain chemical compounds, as will bedescribed, such as organometallic compounds and compounds of elementsselected from Groups 1-16. In one embodiment, the selectivation of thezeolite materials including the silicate-based materials can beaccomplished using compounds including, but not necessarily limited tosilicon, phosphorus, boron, antimony, magnesium compounds, coke, and thelike, and mixtures thereof.

Other silicate-based materials suitable for the second component includezeolite bound zeolites as described in WO 97/45387, incorporated hereinby reference. Zeolite bound zeolite catalysts useful in the presentinvention concern first crystals of an acidic intermediate pore sizefirst zeolite and a binder comprising second crystals of a secondzeolite. Unlike zeolites bound with amorphous material such as silica oralumina to enhance the mechanical strength of the zeolite, the zeolitebound zeolite catalyst suitable for use in the present process does notcontain significant amounts of non-zeolitic binders.

The first zeolite used in the zeolite bound zeolite catalyst is anintermediate pore size zeolite. Intermediate pore size zeolites have apore size from about 5 to about 7 Å and include, for example, AEL, MFI,MEL, MFS, MEI, MTW, EUO, MTT, HEU, FER, and TON structure type zeolites.

These zeolites are described in Atlas of Zeolite Structure Types, eds.W. H. Meier and D. H. Olson, Butterworth-Heineman, Third Edition, 1992,which is hereby incorporated by reference. Examples of specificintermediate pore size zeolites include, but are not limited to, ZSM-5,ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48, ZSM-50,and ZSM-57. Preferred first zeolites are galliumsilicate zeolites havingan MFI structure and aluminosilicate zeolites having an MFR structure.

The second zeolite will usually have an intermediate pore size and haveless activity than the first zeolite. Preferably, the second zeolitewill be substantially non-acidic and will have the same structure typeas the first zeolite. The preferred second zeolites are aluminosilicatezeolites having a silica to alumina mole ratio greater than 100 such aslow acidity ZSM-5. If the second zeolite is an aluminosilicate zeolite,the second zeolite will generally have a silica to alumina mole ratiogreater than 200:1, e.g., 500:1; 1,000:1, etc., and in some applicationswill contain no more than trace amounts of alumina. The second zeolitecan also be silicalite, i.e., a MFI type substantially free of alumina,or silicalite 2, a MEL type substantially free of alumina. The secondzeolite is usually present in the zeolite bound zeolite catalyst in anamount in the range of from about 10% to 60% by weight based on theweight of the first zeolite and, more preferably, from about 20% toabout 50% by weight.

The second zeolite crystals preferably have a smaller size than thefirst zeolite crystals and more preferably will have an average particlesize from about 0.1 to about 0.5 microns. The second zeolite crystals,in addition to binding the first zeolite particles and maximizing theperformance of the catalyst will preferably intergrow and form anover-growth which coats or partially coats the first zeolite crystals.Preferably, the crystals will be resistant to attrition.

The zeolite bound zeolite catalyst suitable for the process of thepresent invention is preferably prepared by a three step procedure. Thefirst step involves the synthesis of the first zeolite crystals prior toconverting it to the zeolite bound zeolite catalyst. Next, asilica-bound aluminosilicate zeolite can be prepared preferably bymixing a mixture comprising the aluminosilicate crystals, a silica gelor sol, water and optionally an extrusion aid and, optionally, the metalcomponent until a homogeneous composition in the form of an extrudablepaste develops. The final step is the conversion of the silica presentin the silica-bound catalyst to a second zeolite which serves to bindthe first zeolite crystals together.

As noted, aluminophosphate-based materials may be used in conjunctionwith metal oxides for aromatic alkylation with syngas.Aluminophosphate-based materials usually have lower acidity compared tosilicate-based materials. The lower acidity eliminates many sidereactions, raises reactants' utilization, and extends catalyst life. Inaddition, some of the medium-pore aluminophosphate-based materials haveunique channel structures that could generate the desirable shapeselectivity.

Further, catalytic reaction systems suitable for this invention includealuminophosphate-based materials and amorphous compounds.Aluminophosphate-based materials are made of alternating AlO₄ and PO₄tetrahedra. Members of this family have 8- (e.g. AlPO₄-12, -17, -21,-25, -34, -42, etc.), 10- (e.g. AlPO₄-11, 41, etc.), or 12- (AlPO₄-5,-31, etc.) membered oxygen ring channels. Although AlPO₄s are neutral,substitution of Al and/or P by cations with lower charge introduces anegative charge in the framework, which is countered by cationsimparting acidity.

By turn, substitution of silicon for P and/or a P—Al pair turns theneutral binary composition (ie. Al, P) into a series ofacidic-ternary-composition (Si, Al, P) based SAPO materials, such asSAPO-5, -11, -14, -17, -18, -20, -31, -34, -41, -46, etc. Acidic ternarycompositions can also be created by substituting divalent metal ions foraluminum, generating the MeAPO materials. Me is a metal ion which can beselected from the group consisting of, but not limited to, Mg, Co, Fe,Zn and the like. Acidic materials such as MgAPO (magnesium substituted),CoAPO (cobalt substituted), FeAPO (iron substituted), MnAPO (manganesesubstituted), ZnAPO (zinc substituted) etc. belong to this category.Substitution can also create acidic quaternary-composition basedmaterials such as the MeAPSO series, including FeAPSO (Fe, Al, P, andSi), MgAPSO (Mg, Al, P, Si), MnAPSO, CoAPSO, ZnAPSO (Zn, Al, P, Si),etc. Other substituted aluminophosphate-based materials include EIAPOand EIAPSO (where EI=B, As, Be, Ga, Ge, Li, Ti, etc.) As mentionedabove, these materials have the appropriate acidic strength forsyngas/aromatic alkylation. The more preferred aluminophosphate-basedmaterials of this invention include 10- and 12-membered ring materials(SAPO-11, -31, -41; MeAPO-11, -31, -41; MeAPSO-11, -31, 41; EIAPO-11,-31, -41; EIAPSO-11, -31, -41, etc.) which have significant shapeselectivity due to their narrow channel structure.

It has been discovered that it may not be necessary for thealuminophosphate-based materials to be processed in a para-alkylselectivation, step for good selectivity prior to producing para-xylene.Optionally, however, these aluminophosphates may be para-alkylselectivated or modified to be more selective through the use of certainchemical compounds, as will be described, such as organometalliccompounds and compounds of elements selected from Groups 1-16. In oneembodiment, the para-alkyl selectivation of the zeolite materialsincluding the aluminophosphate-based materials can be accomplished usingcompounds including, but not necessarily limited to silicon, phosphorus,boron, antimony, magnesium compounds, coke, and the like, and mixturesthereof.

The composition of the proposed catalytic reaction systems may be from 5wt. % metals or metal oxides first component/95 wt. % silicate-basedmaterial or aluminophosphate-based material second component, to 95 wt.% metals or metal oxides first component/5 wt. % silicate-based materialor aluminophosphate-based material second component. The preparation ofthe catalytic reaction systems can be accomplished with severaltechniques known to those skilled in the art. Some examples are givenbelow.

Para-alkyl selectivation involves the treatment of the above mentionedcatalytic reaction system materials with proper chemical compounds. Somepara-alkyl selectivation treatments are known, e.g. using siliconcompounds. Other compounds that may be used include, but are not limitedto compounds of phosphorus, boron, antimony, magnesium, and the like,and coke, and the like. Para-alkyl selectivation treatments of thematerials of the above catalytic reaction systems, such as by using themetals/metal oxides first component to selectivate, can be carried outeither prior to the selective formation of PX (ex situ) or during the PXformation (in situ). In the in situ embodiment, the selectivating agentsare added with the feed to the reactor containing a catalytic reactionsystem.

In more detail, in one non-limiting embodiment, the technique forselectivating the materials useful in the method of this invention isbased on the consideration that by depositing on a silicate-basedmaterial or aluminophosphate-based material one or more than one of theorganometallic compounds which are too bulky to enter the channels (orother para-alkyl selectivating agents), one should be able to modifyonly the external surface and regions around channel mouth. The factthat the para-alkyl selectivation agent does not enter the channelspreserves the active sites inside the channels. Since the channel activesites account for the majority of the total active sites, theirremaining active prevents any significant loss of reactivity orconversion.

It will be understood that the para-alkyl selectivation techniques ofthis invention may be practiced before or after the silicate-basedmaterials or aluminophosphate-based materials are mixed with or combinedchemically or physically with metals or metal oxides. That is, in someembodiments, the silicate-based materials and aluminophosphate-basedmaterials may be para-alkyl selectivated before combination with metalsor metal oxides. In other embodiments, silicate-based materials andaluminophosphate-based materials may be para-alkyl selectivated aftercombination with metals or metal oxides. The former process might betermed “pre-selectivation”, while the latter process may be termed“post-selectivation”.

One type of the bulky organometallic compounds suitable for para-alkylselectivating 10-member-ring zeolites, such as the ZSM family (e.g.ZSM-5, -11, -22, -48, etc.), mordenite, etc., is the salts of largeorganic anions and metallic cations. The organic anions can be selectedfrom molecules containing carboxylic and/or phenolic functional groups,including but not limited to phthalate, ethylenediaminetetraacetic acid(EDTA), vitamin B-5, trihydroxy benzoic acid, pyrogallate, salicylate,sulfosalicylate, citrate, naphthalene dicarboxylate, anthradiolate,camphorate, and others. The metallic cations can be selected from theelement(s) of Groups 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,and 16 (new IUPAC notation). Other compounds for para-alkylselectivating the silicate-based and aluminophosphate-based materialsinclude, but are not necessarily limited to silicon, phosphorus, boron,antimony, magnesium compounds, coke, and the like, and mixtures thereof.

Para-alkyl selectivation of silicate-based materials andaluminophosphate-based materials with the above mentioned organometallicsalts can be accomplished by various means. For example, one can useimpregnation of a solution of an organometallic salt onto asilicate-based material or aluminophosphate-based materials. Eitherwater or any suitable organic solvent can be used. Addition ofnon-metallic salts and/or adjustments of pH to facilitate the treatmentare optional. Heat will be provided to drive off the solvent leavingbehind a material coated homogeneously with the organometallic salt.Drying and calcination of the coated zeolite or aluminophosphate-basedmaterials at appropriate temperatures will turn the salt into metaloxide. Alternatively, one can use a dry-mix technique, which involvesmixing directly a zeolite in the form of powder or particles with aorganometallic salt also in the form of powder or particles without theuse of any solvent. The mixture will then be subjected to heattreatment, which facilitates the dispersion of the salt over thematerial and eventually turn the salt into metal oxide.

Known techniques for ex situ and in situ catalytic reaction systemmodification can be incorporated into producing the para-alkylselectivated catalytic reaction systems of the present invention inaccordance herewith, such as those seen in U.S. Pat. Nos. 5,476,823 and5,675,047, incorporated herein by reference.

In one embodiment, the same metals and/or metal oxide components used inthe catalytic reaction system can be used alone or together toselectivate the silicate-based material or aluminophosphate-basedmaterial components.

The catalytic reaction systems can be prepared by adding solutions ofmetal salts either in series to or as a mixture with the fine powder orparticles such as extrudates, spheres, etc. of the unselectivatedsilicate-based materials having one dimensional channel structures, oroptionally ex situ para-alkyl selectivated silicate-based materials,unselectivated aluminophosphate-based materials, or optionally ex situpara-alkyl selectivated aluminophosphate-based materials, untilincipient wetness is reached. The solvent (water or other solvents) canbe evacuated under heat or vacuum using a typical equipment such as arotary evaporator. The final product is dried, calcined, and pelletized,if necessary.

Alternatively, solutions of metal salts and the ex situ para-alkylselectivated fine powder or particles such as extrudates, spheres, etc.of the silicate-based and aluminophosphate-based materials arethoroughly mixed. A dilute basic solution (e.g. ammonia, sodiumcarbonate, potassium hydroxide, etc.) is used to adjust the pH value ofthe mixture to facilitate the precipitation of metal hydroxides andzeolites. The precipitate is filtered and washed thoroughly with water.The final product is dried, calcined, and pelletized, if necessary.

The catalytic reaction systems can also be prepared using physicalmixing. Finely divided powders of metal(s) or metal oxide(s), or powdersof metal(s) or metal oxide(s) supported on any inert materials, aremixed thoroughly with finely divided powder of the ex situ para-alkylselectivated silicate-based materials, unselectivatedaluminophosphate-based materials, or optionally ex situ para-alkylselectivated aluminophosphate-based materials in a blending machine or agrinding mortar. The mixture is optionally pelletized before use.

If the catalytic reaction system is mixed with a binder, such as silicagel or sol or the like, an extrudable paste may be formed. The resultingpaste can be molded, e.g. extruded, and cut into small strands which canthen be dried and calcined.

The catalytic reaction system can also be prepared by mixing physicallythe particles of silicate-based material or aluminophosphate-basedmaterials components and the particles of the metal and/or metal oxidefirst components. The same metals and/or metal oxides can also be usedalone or together to selectivate catalytic reaction systems and thussimultaneously catalyze syngas reactions.

The catalytic reaction system can also be formed by packing the firstand the second components in a stacked-bed manner with some of the firstcomponent in front of the physical or chemical mixture of the first andsecond components.

Prior to exposing the catalytic reaction systems to the feed componentsof toluene and/or benzene, H₂, CO, and/or CO₂ and/or methanol thecatalytic reaction systems can optionally be activated under a reducingenvironment (e.g. 1-80% H₂ in N₂) at 150-500° C., and 1-200 atm(1.01×10⁵-2.03×10⁷ Pa) for 2-48 hours.

The average crystal size of the crystals in the silicate-based materialor aluminophosphate-based materials is preferably from above 0.1 micronto about 100 microns, more preferably from about 1 micron to about 100microns.

Procedures to determine crystal size are known to persons skilled in theart. For instance, crystal size may be determined directly by taking asuitable scanning electron microscope (SEM) picture of a representativesample of the crystals.

The methylation process can be carried out as a batch type,semi-continuous or continuous operation utilizing a fixed, moving bed,or CSTR catalytic reaction system, with or without recycle. Multipleinjection of the methylating agent may be employed. The methylatingagent includes CO, CO₂ and H₂ and/or CH₃OH and derivatives thereof. Themethylating agent reacts with benzene to form toluene. Toluene reactswith the methylating agent to form a xylene, preferably PX in thisinvention. In one preferred embodiment of the invention, methanol as themethylating agent is not separately added but is formed in situ.

Toluene and/or benzene and the methylating agent(s) are usually premixedand fed together into the reaction vessel to maintain the desired ratiobetween them with no local concentration of either reactant to disruptreaction kinetics. Individual feeds can be employed, however, if care istaken to insure good mixing of the reactant vapors in the reactionvessel. Optionally, instantaneous concentration of methylating agent canbe kept low by staged additions thereof. By staged additions, the ratiosof toluene and/or benzene to methylating agent concentrations can bemaintained at optimum levels to give good aromatic compound conversionsand better catalytic reaction system stability. Hydrogen gas can alsoserve as an anticoking agent and diluent.

The method of this invention, particularly when using para-alkylselectivated catalytic reaction systems, stabilizes catalytic reactionsystem performance and increases catalytic reaction system life. Thatis, catalytic reaction system deactivation is slowed and even prevented.With properly para-alkyl selectivated catalytic reaction systems, it isexpected that the catalytic reaction system may not have to beregenerated at all. This is in part due to the silicate-based materialsand aluminophosphate-based materials being para-alkyl selectivated. Withproduction selective to PX, less by-products, such as heavy aromatics,are formed which would deactivate the catalytic reaction systems. Thischaracteristic is not shown or taught by the prior art.

Further, in one non-limiting embodiment of the invention, there is abelief that the catalytic reaction systems of this invention have thecapability of preventing or reducing the side reactions of themethylating agents with themselves, and in particular that thepara-alkyl selectivated catalytic reaction systems function to catalyzemore than one reaction, that is, that a syngas reaction is catalyzed toform methylating agents which react with benzene and/or toluene toproduce PX. However, because the methylating agent is produced on alocal, molecular scale, its concentrations are very low (as contrastedwith feeding a methylating agent as a co-reactant). It has beendemonstrated that feeding a blend of methylating agent and toluene tomake PX increases coke build-up and hence catalytic reaction systemdeactivation.

In one non-limiting embodiment of the invention, the catalyst activitydecrease is less than 0.5% toluene and/or benzene conversion pet day,preferably less than 0.1%.

In carrying out the process, the feed mixtures can be co-fed into areactor containing one of the above mentioned catalytic reactionsystems. The catalytic reaction system and reactants can be heated toreaction temperatures separately or together. Reaction can be carriedout at a temperature from about 100-700° C., preferably from about200-600° C.; at a pressure from about 1-300 atm (1.01×10⁵-3.04×10⁷ Pa),preferably from about 1-200 atm (1.01×10⁵-2.03×10⁷ Pa); and at a flowrate for about 0.01-100 h⁻¹ LHSV, preferably from about 1-50 h⁻¹ LHSV ona liquid feed basis. The composition of the feed, i.e. the mole ratio ofH₂/CO(and/or CO₂)/aromatic can be from of about 0.01-10/0.01-10/0.01-10,preferably from about 0.1-10/0.1-10/0.1-10.

As noted, typical methylating agents include or are formed from, but arenot necessarily limited to hydrogen together with carbon monoxide and/orcarbon dioxide, and/or methanol, but also dimethylether, methylchloride,methylbromide, and dimethylsulfide.

It is conceivable that in the scenarios described above, the toluene canbe pure, or in a mixture with benzene. The benzene may alkylate totoluene, and/or ultimately to PX, with or without recycle. The presenceof benzene may also enhance heat and/or selectivity control.

The method of this invention is expected to tolerate many differentkinds of feed. Unextracted toluene, which is a mixture of toluene andsimilar boiling range olefins and paraffins, is preferred in oneembodiment. For example, premium extracted toluene, essentially puretoluene, and extracted aromatics, essentially a relatively pure mixtureof toluene and benzene, may also be used. Unextracted toluene andbenzene which contains toluene, benzene, and olefins and paraffins thatboil in a similar range to that of toluene or benzene, may also beemployed. When unextracted feedstocks are used, it is important to crackthe paraffins and olefins into lighter products that can be easilydistilled. For example, the feed may contain one or more paraffinsand/or olefins having at least 4 carbon atoms; the catalytic reactionsystems have the dual function to crack the paraffins and/or olefins andmethylate benzene or toluene to selectively produce PX.

Indeed, some of the catalytic reaction systems of this invention may bemultifunctional in some embodiments, catalyzing a reaction or reactionsof CO, H₂, and/or CO₂ and/or methanol to produce a methylating agent,catalyzing the selective methylation of toluene and/or benzene toproduce PX, and catalyzing the cracking of paraffins and olefins intorelatively lighter products.

The method of this invention is capable of producing mixtures of xyleneswhere PX comprises at least 30 wt. % of the mixture, preferably at least36 wt. %, and most preferably at least 48 wt. %. The method of thisinvention is also capable of converting at least 5 wt. % of the aromaticcompound to a mixture of xylenes, preferably greater than 15 wt. %.

para-Xylene may be recovered from the process stream, for example bycrystallization, for use in products such as terephthalic acid, dimethylterephthalate acid, polyethylene terephthalate polymer, and the like,which in turn can be used to make synthetic fibers. There are threecommercial techniques to recover PX, fractionation, adsorption (PAREXzeolite), and crystallization. In a preferred embodiment of theinvention, combinations of these recovery techniques may used to lowercapital costs. In another preferred embodiment of the invention,crystallization is used, particularly single-stage crystallization.Single-stage crystallization simply means that only one crystallizationstep is used on the product from the inventive process, which would be asimple and relatively inexpensive procedure. Because of the high qualityproduct produced by the inventive process, it is expected that the PXproportion in the product from the inventive process may be 80% or more,while after one crystallization step, the proportion may be 99% orhigher.

The following examples will serve to illustrate the processes and meritsof the present invention. It is to be understood that these examples aremerely illustrative in nature and that the present process is notnecessarily limited thereto.

EXAMPLE I

This example illustrates one of the methods in preparing a catalyticreaction system. The catalytic reaction system comprises (1) Cr and Znmixed metal oxides; and (2) H-ZSM-5 zeolite with a SiO₂/AlO₂ molar ratioof 30 (obtained from PQ Corporation, Valley Forge, Pa.). The Cr and Znmixed metal oxides were prepared by co-precipitation of Cr(NO₃)₃ andZn(NO₃)₂ with NH₄OH. 7.22 grams of Cr(NO₃)₃ and 13.41 grams of Zn(NO₃)₂were dissolved in 100 ml distilled water separately. The two solutionswere then mixed together. NH₄OH was slowly added into the mixed solutionwith stirring until the pH value of the solution reached about 8. Theprecipitate was filtered and recovered. This precipitate was dried at atemperature of 120° C. for 12 hours, and then calcined in air at 500° C.for 6 hours. These Cr/Zn mixed metal oxides were ground into powders.

The catalytic reaction system was prepared by physically mixing powdersof a composition of 50% (w/w) Cr/Zn mixed metal oxides and 50% (w/w)H-ZSM-zeolite. Powders of 2.0 grams of Cr/Zn mixed metal oxides and 2.0grams of H-ZSM-5 zeolite were mixed thoroughly in a grinding mortar. Themixed catalytic reaction system powders were pelletized and screened to8-12 mesh particles.

EXAMPLE II

This example shows that the synthesis of xylenes with syngas alkylationof toluene can be achieved in a catalytic process as disclosed by priorart. However, this example indicates that such a process cannot achievehigh para-xylene selectivity when the aluminosilicate component in thecatalytic reaction system is not modified for shape selectivity. Thecatalytic reaction system was prepared as in Example I. The catalyticreaction system was reduced at 350° C. under 5% H₂ (balanced with 95%N₂) for 16 hours at 1 atm prior to reaction.

The catalytic reaction system was evaluated with co-feed of syngas (COand H₂) and toluene with a composition of H₂/CO/toluene of 2/1/0.5(molar ratio), a temperature of about 450° C., and a pressure of about18 atm (i.e., 250 psig). The WHSV (Weight Hourly Space Velocity) wasabout 3 h⁻¹ for toluene with respect to the catalytic reaction system.Test results are given in Table 1. Similar to prior art reported, theselectivity of para-xylene in xylenes is about 25%, which is close toequilibrium, with toluene conversion of 28.6% and xylene selectivity of71.1%.

TABLE 1 Synthesis of PX using Zeolite not Selectivated CO H₂ TolueneXylene PX conv. % conv. % conv. % select. % select. % 31.7 17.1 28.671.1 25.0

EXAMPLE III

This example illustrates the poor product quality derived from aconventional metal oxides/aluminosilicate system. The catalytic reactionsystem was a physical mixture of 50 wt % of ZSM-5 in the form of powder(CBV8020, an aluminosilicate zeolite obtained from PQ Corp., ValleyForge, Pa.) and 50 wt % of a composite of oxides of copper, zinc, andaluminum also in the form of powder (C-79, obtained from UCI Inc.,Louisville, Ky.). The two components were mixed thoroughly, pelletized,and screened to 8/12 mesh particles. The catalytic reaction systemparticles were packed in a stainless steel reactor and reduced with agas mixture of 2% hydrogen in 98% nitrogen at 250 C. and 1 atm (1.01×10⁵Pa) for 16 hours. The feed stream was a mixture of syngas and toluenehaving a molar ratio of 1:1:0.47 (hydrogen:carbon monoxide:toluene). Thereaction conditions were set at 350° C. and 350 psig. A distribution ofthe liquid hydrocarbon products is given in Table 2. It is seen that thecatalytic reaction system made 39.80% of undesirable heavy aromaticcompounds (A9, A10, & A11+). The lack of para-selectivity was indicatedby the near equilibrium concentration (24.14%) of PX in thexylene-fraction products.

TABLE 2 Conventional Metal Oxides/Aluminosilicate System Products wt %A₈-Fraction, wt % Non-aromatics 1.54 Benzene 1.07 Ethylbenzene 0.40 0.69para-Xylene 13.90 24.14 meta-Xylene 30.36 52.72 ortho-Xylene 12.93 22.45A9-A10 27.66 A11+ 12.14

EXAMPLE IV

This example illustrates the superior performance of the proposed metaloxides/silicon-aluminophosphate system of this invention. The catalyticreaction system was a physical mixture of 50 wt% of SAPO-11 material inthe form of powder (an aluminophosphate material obtained from UOP) and50 wt % of the same C-79 composite as in Example III. The two componentswere mixed thoroughly, pelletized, and screened to 8/12 mesh particles.The catalytic reaction system particles were packed in a stainless steelreactor and reduced with a gas mixture of 2% hydrogen in 98% nitrogen at250° C. and 1 atm (1.01×10⁵ Pa) for 16 hours. The feed stream was amixture of syngas and toluene having a molar ratio of 1:1:0.45(hydrogen:carbon monoxide:toluene). The reaction conditions were set at350° C. and 350 psig. A distribution of the liquid hydrocarbon productsis given in Table 3. It is seen that the catalytic reaction system mademuch less undesirable heavy aromatic compounds (11.29% for A9, A10, &A11+). The improvement in para-selectivity was indicated by themuch-higher-than-equilibrium concentration (45.52%) of PX in thexylene-fraction products.

TABLE 3 Metal Oxides/Silicon-Aluminophosphate System of the InventionProducts wt % A₈-Fraction, wt % Non-aromatics 21.11 Benzene 1.25Ethylbenzene 1.09 1.64 para-Xylene 30.20 45.52 meta-Xylene 21.81 32.87ortho-Xylene 13.25 19.97 A9-A10 9.47 A11+ 1.82

EXAMPLE V

This example illustrates the preparation of para-alkyl selectivatedZSM-5 zeolite with magnesium oxide as the selectivating agent. 11.68grams of magnesium hydroxide was mixed with distilled water. To thesolution was added 20.44 grams of ammonium nitrate and 33.54 grams ofphthalic acid in sequence. The mixture was heated to obtain a clearsolution, which was cooled to room temperature before use. 14.80 gramsof the solution was mixed with 7.77 grams of a ZSM-5 zeolite (SiO₂/AlO₂of 50). The mixture was heated to evaporate the water solvent. Theremaining solid was dried at 120° C. for 12 hours and calcined at 500°C. for 8 hours with air purge. The para-alkyl selectivated ZSM-5 zeolitecontained approximately 9 wt. % of magnesium oxide.

EXAMPLE VI

This example illustrates the preparation of another type of thecatalytic reaction system. The catalytic reaction system comprises (1)Mn and Zn mixed metal oxides, and (2) MgO modified H-ZSM-5 zeolite witha SiO₂/AlO₂ of 38. The same preparation procedures as that given inExample V were used. The Mn and Zn mixed metal oxides were prepared byco-precipitation of Mn(NO₃)₂ and Zn(NO₃)₂ with NH₄OH. 4.14 grams ofMn(NO₃)₂ and 13.44 grams of Zn(NO₃)₂ were dissolved in 100 ml distilledwater separately. The two solutions were then mixed together. NH₄OH wasslowly added into the mixed solution with stirring until the pH value ofthe solution reached about 7.5. The precipitate was filtered andrecovered. This precipitate was dried at a temperature of 120° C. for 12hours, and then calcined in air at 500° C. for 6 hours. These Mn/Znmixed metal oxides were ground into powders.

The catalytic reaction system was prepared by physically mixing powdersof a composition of 50% (w/w) Mn/Zn mixed metal oxides and 50% (w/w) MgOmodified H-ZSM-5 zeolite. Powders of 2.0 grams of Mn/Zn mixed metaloxides and 2.0 grams of MgO modified H-ZSM-5 zeolite were mixedthoroughly in a grinding mortar. The mixed catalytic reaction systempowders were pelletized and screened to 8-12 mesh particles.

EXAMPLE VII

This example illustrates that metal oxides other than Cr/Zn mixed metaloxides are also suitable as one of the components in the catalyticreaction system used in the xylenes synthesis with syngas alkylation oftoluene. In addition, this example demonstrates that high para-xyleneselectivity can be obtained when the aluminosilicate component in thecatalytic reaction system is modified for shape selectivity. Thecatalytic reaction system was prepared as in Example VI. The catalyticreaction system was reduced at 350° C. under 5% H₂ (balanced with 95%N₂) for 16 hours at 1 atm prior to reaction.

The reaction was conducted under similar conditions to those in ExampleII. Test results are given in Table 4. The para-xylene selectivity inxylenes is about 76.0% with toluene conversion of 10.9% and xyleneselectivity of 85.4%. Compared to Example II, the para-xyleneselectivity is significantly enhanced when the aluminosilicate componentis modified for shape selectivity.

TABLE 4 Synthesis of PX using Zeolite Modified for Shape Selectivity COH₂ Toluene Xylene PX conv. % conv. % conv. % select. % select. % 11.75.6 10.9 85.4 76.0

EXAMPLE VIII

This example illustrates that the toluene conversion can be increasedwith a similar high para-xylene selectivity when the reaction operationconditions are optimized. The catalytic reaction system used in thisexample was comprised of a composition of (1) 50% (w/w) Cr, Zn, and Mgmixed metal oxides, and (2) 50% (w/w) MgO modified H-ZSM-5 zeolite witha SiO₂/AlO₂ of 38. The Cr, Zn, and Mg mixed metal oxides were preparedin a similar method as described in Example I with co-precipitation ofCr(NO3)₃, Zn(NO₃)₂, and Mg(NO₃)₂ with NH₄OH. The magnesiumoxide-modified ZSM zeolite was prepared as described in Example V. Thecatalytic reaction system was prepared by physical mixing as describedin Example I. The catalytic reaction system was reduced at 350° C. under5% H₂ (balanced with 95% N₂) for 16 hours at 1 atm (1.01×10⁵ Pa) priorto reaction.

The catalytic reaction system was evaluated with co-feed of syngas (COand H₂) and toluene with a varied composition of H₂/CO/toluene, atemperature from 450-490° C., and a pressure in the range of 18-28 atm(i.e. 250-390 psig 1.82×10⁶-2.83×10⁶). The WHSV (Weight Hourly SpaceVelocity) varied from 1.5-6 h⁻¹ for toluene with respect to thecatalytic reaction system. Some of the test results are shown in Table5. As shown in Table 5, a toluene conversion of 34% was achieved with asimilar para-xylene selectivity when the reaction was operated at atemperature of ca. 460° C., a pressure of ca. 28 atm (390 psig, 2.83×10⁶Pa) and a WHSV of ca. 1.5 h⁻¹ for toluene with respect to catalyticreaction system.

TABLE 5 Synthesis of PX using Zeolite Modified for Shape SelectivityReaction Temperature, ° C. 460 460 460 475 Reaction Pressure, psig 250390 250 250 Feed Composition, 2/1/0.25 2/1/0.25 2/1/0.5 2/1/0.5 moleratio WHSV, h⁻¹ (Tol./Catalyst) 1.5 1.5 3 3 CO conv. % 18.4 29.2 17.418.1 H₂ conv. % 6.6 9.4 7.4 7.6 Toluene conv. % 26.0 34.7 13.6 15.5Xylene select. % 84.2 80.1 82.4 86.3 PX select. % 74.5 75.2 88.0 85.1

EXAMPLE IX

This example illustrates the problems of low methanol selectivity andfast catalytic reaction system deactivation associated with a lowaromatic/methanol ratio and one-time methanol injection. The catalyticreaction system was extrudates of SAPO-11 material obtained from UOP.The extrudates were ground and screened to 8-12 mesh and calcined at550° C. under air for 16 hours prior to use. The catalytic reactionsystem was evaluated at 350° C., 25 atm (350 psig), and 8 h⁻¹ WHSV. Thefeed was a mixture of toluene/methanol with a molar ratio of 3.6. Testresults are given in Table 6. It is seen that the methanol selectivitydecreased from 70.0% to 55.0% over a test period of 24 hours.Furthermore, the system was experiencing a severe catalytic reactionsystem deactivation as indicated by the decreasing toluene conversionfrom 18.5% to 15.1%.

TABLE 6 Synthesis of PX with Low Methanol Selectivity and CatalyticReaction System Deactivation Toluene/Methanol (mole) 3.6 Hours on Stream2 24 Toluene Total Conversion 18.5% 15.1% Toluene Conversion due toDisproportionation 0% 0% Toluene Conversion due to Methylation 18.5%15.1% Methanol Total Conversion 100% 97.0% Methanol consumed by mono-and multiple 70.0% 55.0% methylation of toluene Methanol consumed byother Reactions 30.0 % 42.0%

EXAMPLE X

This example demonstrates the problems of fast catalytic reaction systemdeactivation for MgO para-alkyl selectivated H-ZSM-5 in toluenemethylation with low toluene/methanol ratio and one-time methanolinjection. The catalytic reaction system was MgO-para-alkyl selectivatedH-ZSM-5 with a SiO₂/AlO₂ ratio of 38. The same preparation procedure asthat given in Example V was used. The catalytic reaction system waspelletized and screened to 40-60 mesh (0.042-0.025 cm). The catalyticreaction system was tested at 460° C., 1 atm, and 14 h⁻¹ WHSV. The feedwas a mixture of toluene/methanol with a molar ratio of 1.0. The resultspresented in Table 7 indicate that although MgO para-alkyl selectivationof H-ZSM-5 improves the para-xylene selectivity, this catalytic reactionsystem still exhibits serious catalytic reaction system deactivation asindicated by the decreasing toluene conversion from 20.5% to 8.5%.

TABLE 7 Synthesis of PX Showing Catalytic Reaction System DeactivationToluene/Methanol (molar ratio) 1/1 Hours on Stream 0.5 2 2 2.5 TolueneConversion, % 19.3 19.8 20.5 8.5 Methanol Conversion, % 100 100 100 99.6Xylene Selectivity, % 76.7 76.4 84.1 86.1 Para-Xylene Selectivity, %83.3 83.3 86.5 76.3

EXAMPLE XI

This example demonstrates that the catalytic reaction system wouldsuffer from deactivation for syngas methylation of toluene if thealuminosilicate component in the catalytic reaction system is notproperly para-alkyl selectivated. The test was conducted in the samemanner as Example II. The reaction was monitored as time-on-stream, andthe results are shown in Table 8. The catalytic reaction system displayssome deactivation over a period of 18 hours as indicated by thedecreasing toluene conversion from 35.3% to 28.6%.

TABLE 8 Synthesis of PX Showing Catalytic Reaction System DeactivationCO/Toluene (molar ratio) 2/1/0.5 Hours on Stream 2 9.5 18.2 TolueneConversion, % 35.3 31.1 28.6 CO Conversion, % 33.6 31.4 31.7 H₂Conversion, % 17.8 16.4 17.1 Xylene Selectivity, % 67.4 69.8 71.1Para-Xylene Selectivity, % 24.8 24.9 25.0

EXAMPLE XII

This example illustrates that the process disclosed in this inventionhas a much higher activity maintenance for PX synthesis than theconventional methanol-toluene methylation process.

The catalytic reaction system used in this example comprised (1) Cr andZn mixed metal oxides, and (2) MgO modified H-ZSM-5 zeolite with aSiO₂/AlO₂ of 38. The Cr and Zn mixed metal oxides were prepared asdescribed in Example I. The magnesium oxide-modified ZSM zeolite wasprepared as described in Example V. The Cr/Zn mixed metal oxides wereground into powders. The catalytic reaction system was prepared byphysically mixing powders of a composition of (1) 34% (w/w) Cr and Znmixed metal oxides, and (2) 66% MgO modified H-ZSM-5 zeolite. The mixedcatalytic reaction system powders were pelletized and screened to 8-12mesh particles. The catalytic reaction system was reduced at 350° C.under 5% H₂ (balanced with 95% N₂) for 16 hours at 1 atm (1.01×10⁵ Pa)prior to reaction. The organometallic modifier was magnesium phthalate.

The catalytic reaction system was evaluated with similar operationconditions as those in Example II. Test results are given in Table 9. Itis seen that the catalytic reaction system had a stable activity fortoluene conversion with stable PX selectivity.

TABLE 9 Higher Activity Maintenance for Para-Xylene SynthesisH₂/CO/Toluene (molar ratio) 2/1/0.5 Hours on Stream, h 5.5 24 91.5 120Toluene Conversion, % 17.0 18.0 17.4 17.1 CO Conversion, % 20.5 20.717.9 17.8 H₂ Conversion, % 8.5 9.3 9.1 9.1 Xylene Selectivity, % 76.580.2 80.6 80.5 Para-Xylene Selectivity, % 63.4 67.0 71.4 75.2

EXAMPLE XIII

This example illustrates the feasibility of using unextracted toluene asfeed for syngas alkylation of toluene with the catalytic reaction systemdisclosed in this invention. The catalytic reaction system used in thisexample comprised (1) mixed Cr and Zn oxides, and (2) a MgO modifiedH-ZSM-5 zeolite prepared using the methods described in Example V. TheCr and Zn mixed metal oxides were prepared as described in Example I.These Cr/Zn mixed metal oxides were ground into powders. The catalyticreaction system was prepared by physically mixing powders of acomposition of (1) 50% (w/w) mixed Cr and Zn oxides, and (2) 50% MgOmodified H-ZSM-5 zeolite. The mixed catalytic reaction system powderswere pelletized and screened to 8-12 mesh particles. The catalyticreaction system was reduced at 350° C. under 5% H₂ (balanced with 95%N₂) for 16 hours at 1 atm prior to reaction.

The catalytic reaction system was tested first with a co-feed of syngasand toluene, and then with a co-feed of syngas and a toluene/heptanemixture at weight percent of 70%/30%. The reaction was conducted at atemperature of about 460° C. and a pressure of about 21.5 atm (i.e., 300psig 2.1×10⁶ Pa). The WHSV was about 1.5 h⁻¹ for toluene andtoluene/heptane mixture with respect to the catalytic reaction system.The results presented in Table 10 indicate that the catalytic reactionsystem is able to carry out heptane cracking reaction and toluenemethylation reaction simultaneously. The system demonstrated a goodactivity maintenance for both reactions. This feature implies that thecatalytic reaction system could be used to process unextracted toluene.

TABLE 10 Simultaneous Selectivity to PX and Heptane Cracking ShowingCatalytic reaction system Stability H₂/CO/Toluene + Feed H₂/CO/TolueneHeptane Composition (molar ratio) 2/1/0.25 2/1/0.25 2/1/0.25 2/1/0.25Hours on Stream 18 73 89 118 Toluene Conversion, % 27.4 26.8 32.7 34.2Heptane Conversion, % — — 65.7 65.0 CO Conversion, % 34.1 35.0 38.4 38.3H₂ Conversion, % 10.6 14.9 20.7 13.6 Xylene Selectivity, % 85.6 83.755.5 55.2 Para-Xylene Selectivity, % 64.2 65.7 64.9 65.5

In the foregoing specification, the invention has been described withreference to specific embodiments thereof, and has been demonstrated aseffective in providing methods for directly and selectively producing PXfrom benzene and/or toluene and hydrogen together with CO and/or CO₂,using a catalytic reaction system. However, it will be evident thatvarious modifications and changes can be made thereto without departingfrom the broader spirit or scope of the invention as set forth in theappended claims. Accordingly, the specification is to be regarded in anillustrative rather than a restrictive sense. For example, specificcombinations of catalyst components, other than those specificallytried, in other proportions or ratios or mixed in different ways,falling within the claimed parameters, but not specifically identifiedor tried in a particular method to improve the PX selectivity herein,are anticipated to be within the scope of this invention. Further,various combinations of reactants, catalytic reaction systems, catalystmodifiers, and control techniques not explicitly described butnonetheless falling within the appended claims are understood to beincluded.

What is claimed is:
 1. A method for forming para-xylene (PX) comprisingsimultaneously forming a methylating agent from a combination selectedfrom the group consisting of: CO and H₂, CO₂ and H₂, and CO, CO₂ and H₂;and reacting a feed including an aromatic compound selected from thegroup consisting of toluene, benzene and mixtures thereof with themethylating agent in the presence of a catalytic reaction system whichconverts at least 10% of the aromatic compound to a mixture of xylenes,where PX comprises at least 48% of the mixture of xylenes, and where thecatalytic reaction system comprises: a first component selected from thegroup consisting of metals and metal oxides, where the metal element isselected from the group consisting of the Groups 1, 2, 3, 4, 5, 6, 7, 8,9, 10, 11, 12, 13, 14, 15, and 16 of the Periodic Table of Elements (newIUPAC notation); and a second component selected from the groupconsisting of crystalline or amorphous aluminosilicates havingone-dimensional channel structure, para-alkyl selectivated amorphousaluminosilicates, para-alkyl selectivated substituted aluminosilicates,crystalline or amorphous substituted silicates having one-dimensionalchannel structure, para-alkyl selectivated substituted silicates,crystalline or amorphous aluminophosphates, para-alkyl selectivatedcrystalline or amorphous aluminophosphates, para-alkyl selectivatedzeolite-bound zeolites, para-alkyl selectivated substitutedaluminophosphates, and mixtures thereof.
 2. The method of claim 1 wherethe feed comprises benzene, and where the method further comprises:methylating benzene to toluene, and methylating toluene to PX.
 3. Themethod of claim 1 where the first components and the second componentsare combined in a manner selected from the group consisting ofchemically mixed using solutions, physically mixed, stacked, andcombinations thereof.
 4. The method of claim 1 where thepara-selectivated second component of the catalytic reaction system isformed by para-alkyl selectivation comprising modification with an agentselected from the group consisting of compounds of elements selectedfrom Groups 1 through 16, and mixtures thereof.
 5. The method of claim 4where the compound is an organometallic salt comprising: an organicanion having functional groups selected from the group consisting ofcarboxylic groups, phenolic groups and mixtures thereof; and a metalcation selected from the group consisting of the element(s) of Groups 1,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and 16 (new IUPACnotation).
 6. The method of claim 1 where the para-selectivated secondcomponent of the catalytic reaction system is formed by para-alkylselectivation comprising modification with an agent selected from thegroup consisting of organometallic compounds, silicon compounds,phosphorus compounds, boron compounds, antimony compounds, magnesiumcompounds, and mixtures thereof.
 7. The method of claim 1 where thepara-alkyl selectivated second component of the catalytic reactionsystem is para-alkyl selectivated by modification with the samecomponent as the first component selected from the metals and metaloxides.
 8. The method of claim 1 where the para-alkyl selectivatedsubstituted silicates are selected from the group consisting ofgallosilicates, borosilicates and ferrosilicates.
 9. The method of claim1 further comprising recovering PX.
 10. The method of claim 9 whereinthe PX is recovered by a process selected from the group consisting offractionation, crystallization, adsorption, and combinations thereof.11. The method of claim 10 where the PX recovery is by single-stagecrystallization.
 12. The method of claim 1 where the catalytic reactionsystem functions to catalyze at least one reaction in addition toforming PX.
 13. The method of claim 12 where the feed further comprisesat least one compound selected from the group consisting of paraffinsand olefins having at least 4 carbon atoms and where the catalyticreaction system cracks the paraffin or olefin.
 14. The method of claim 1where the catalytic reaction system activity decrease is less than 0.5%toluene and/or benzene conversion per day.
 15. The method of claim 1where the catalytic reaction system activity decrease is less than 0.1%toluene and/or benzene conversion per day.
 16. The method of claim 1where the conversion of aromatic compound to a mixture of xylenes isgreater than 15%.
 17. A method for forming para-xylene (PX) comprising:providing a catalytic reaction system comprising: a first componentselected from the group consisting of metals and metal oxides, where themetal element is selected from the group consisting of the Groups 1, 2,3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and 16 of the PeriodicTable of Elements; and a second component selected from the groupconsisting of crystalline or amorphous aluminosilicates havingone-dimensional channel structure, para-alkyl selectivated amorphousaluminosilicates, para-alkyl selectivated substituted aluminosilicates,crystalline or amorphous substituted silicates having one-dimensionalchannel structure, para-alkyl selectivated substituted silicates,crystalline or amorphous aluminophosphates, para-alkyl selectivatedcrystalline or amorphous aluminophosphates, para-alkyl selectivatedzeolite-bound zeolites, para-alkyl selectivated substitutedaluminophosphates, and mixtures thereof; simultaneously forming amethylating agent from a combination selected from the group consistingof: CO and H₂, CO₂ and H₂, and CO, CO₂ and H₂; and reacting an aromaticcompound selected from the group consisting of toluene, benzene andmixtures thereof with the methylating agent in the presence of thecatalytic reaction system to produce a xylene fraction having a PXconcentration; and recovering PX where greater than 15% of the aromaticcompound is converted to a xylene fraction and where the PXconcentration recovered in the xylene fraction is greater than 48%. 18.The method of claim 17 where the first components and the secondcomponents are combined in a manner selected from the group consistingof chemically mixed using solutions, physically mixed, stacked, andcombinations thereof.
 19. The method of claim 17 where thepara-selectivated second component of the catalytic reaction system isformed by para-alkyl selectivation comprising modification with an agentselected from the group consisting of compounds of elements selectedfrom Groups 1 through 16, and mixtures thereof.
 20. The method of claim19 where the compound is an salt comprising: an organic anion havingfunctional groups selected from the group consisting of carboxylicgroups, phenolic groups and mixtures thereof; and a metal cationselected from the group consisting of the element(s) of Groups 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and 16 (new IUPAC notation).21. The method of claim 17 where the para-selectivated second componentof the catalytic reaction system is formed by para-alkyl selectivationcomprising modification with an agent selected from the group consistingof organometallic compounds, silicon compounds, phosphorus compounds,boron compounds, antimony compounds, magnesium compounds, and mixturesthereof.
 22. The method of claim 17 where the para-alkyl selectivatedsecond component of the catalytic reaction system is para-alkylselectivated by modification with the same component as the firstcomponent selected from the metals and metal oxides.
 23. The method ofclaim 17 where the PX is recovered by a process selected from the groupconsisting of fractionation, crystallization, adsorption, andcombinations thereof.
 24. The method of claim 23 where the PX recoveryis by single-stage crystallization.
 25. The method of claim 17 where thecatalytic reaction system functions to catalyze at least one reaction inaddition to forming PX, where the feed further comprises at least oneparaffin having at least 7 carbon atoms and where the catalytic reactionsystem cracks the paraffin.
 26. The method of claim 17 where thecatalytic reaction system activity decrease is less than 0.5% tolueneand/or benzene conversion per day.
 27. The method of claim 17 where theconversion of aromatic compound to a mixture of xylenes is greater than15%.
 28. A method for forming para-xylene (PX) comprising simultaneouslyforming a methylating agent from a combination selected from the groupconsisting of: CO and H₂, CO₂ and H₂, and CO, CO₂ and H₂; and reacting afeed including an aromatic compound selected from the group consistingof toluene, benzene and mixtures thereof with the methylating agent inthe presence of a catalytic reaction system which converts at least 10%of the aromatic compound to a mixture of xylenes, where PX comprises atleast 48% of the mixture of xylenes, and where the catalytic reactionsystem comprises: a first component selected from the group consistingof metals and metal oxides, where the metal element is selected from thegroup consisting of the Groups 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, and 16 of the Periodic Table of Elements (new IUPACnotation); and a second component selected from the group consisting ofcrystalline or amorphous aluminosilicates having one-dimensional channelstructure, para-alkyl selectivated amorphous aluminosilicates,para-alkyl selectivated substituted aluminosilicates, crystalline oramorphous substituted silicates having one-dimensional channelstructure, para-alkyl selectivated substituted silicates, crystalline oramorphous aluminophosphates, para-alkyl selectivated crystalline oramorphous aluminophosphates, para-alkyl selectivated zeolite-boundzeolites, para-alkyl selectivated substituted aluminophosphates, andmixtures thereof.
 29. The method of claim 28 where the feed comprisesbenzene and where the method further comprises: methylating benzene totoluene, and methylating toluene to PX.
 30. The method of claim 18 wherethe first components and the second components are combined in a mannerselected from the group consisting of chemically mixed using solutionsphysically mixed, stacked, and combinations thereof.
 31. The method ofclaim 28 where the para-selectivated second component of the catalyticreaction system is formed by para-alkyl selectivation comprisingmodification with an agent selected from the group consisting ofcompounds of elements selected from Groups 1 through 16, and mixturesthereof.
 32. The method of claim 31 where the compound is anorganometallic salt comprising: an organic anion having functionalgroups selected from the group consisting of carboxylic groups, phenolicgroups and mixtures thereof; and a metal cation selected from the groupconsisting of the element(s) of Groups 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,11, 12, 13, 14, 15, and 16 (new IUPAC notation).
 33. The method of claim28 where the para-selectivated second component of the catalyticreaction system is formed by para-alkyl selectivation comprisingmodification with an agent selected from the group consisting oforganometallic compounds, silicon compounds, phosphorus compounds, boroncompounds, antimony compounds, magnesium compounds, and mixturesthereof.
 34. The method of claim 28 where the para-alkyl selectivatedsecond component of the catalytic reaction system is para-alkylselectivated by modification with the same component as the firstcomponent selected from the metals and metal oxides.
 35. The method ofclaim 28 where the para-alkyl selectivated substituted silicates areselected from the group consisting of gallosilicates, borosilicates andferrosilicates.
 36. The method of claim 28 further comprising recoveringPX.
 37. The method of claim 36 wherein the PX is recovered by a processselected from the group consisting of fractionation, crystallization,adsorption, and combinations thereof.
 38. The method of claim 37 wherethe PX recovery is by single-stage crystallization.
 39. The method ofclaim 28 where the catalytic reaction system functions to catalyze atleast one reaction in addition to forming PX.
 40. The method of claim 39where the feed further comprises at least one compound selected from thegroup consisting of paraffins and olefins having at least 4 carbon atomsand where the catalytic reaction system cracks the paraffin or olefin.41. The method of claim 28 where the catalytic reaction system activitydecrease is less than 0.5% toluene and/or benzene conversion per day.42. The method of claim 28 where the catalytic reaction system activitydecrease is less than 0.1% toluene and/or benzene conversion per day.43. The method of claim 28 where the conversion of aromatic compound toa mixture of xylenes is greater than 15%.
 44. A method for formingpara-xylene (PX) comprising simultaneously forming a methylating agentfrom a combination selected from the group consisting of: CO and H₂, CO₂and H₂, and CO, CO₂ and H₂; and reacting a feed including an aromaticcompound selected from the group consisting of toluene, benzene andmixtures thereof with the methylating agent in the presence of acatalytic reaction system which converts at least 10% of the aromaticcompound to a mixture of xylenes, where PX comprises at least 48% of themixture of xylenes, and where the catalytic reaction system comprises: afirst component selected from the group consisting of metals and metaloxides, where the metal element is selected from the group consisting ofthe Groups 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and 16 ofthe Periodic Table of Elements (new IUPAC notation); and a secondcomponent that is a para-alkyl selectivated crystalline aluminosilicateprepared by depositing compounds selected from the group consisting oforganometallic compounds, silicon compounds, phosphorous compounds,boron salts, antimony compounds, magnesium salts, coke, and mixturesthereof, on said aluminosilicate.
 45. The method of claim 44 where thedeposited compounds are converted into oxides.
 46. A method for formingpara-xylene (PX) comprising: providing a catalytic reaction systemcomprising: a first component selected from the group consisting ofmetals and metal oxides, where the metal element is selected from thegroup consisting of the Groups 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, and 16 of the Periodic Table of Elements; and a secondcomponent that is a para-alkyl selectivated crystalline aluminosilicateprepared by depositing compounds selected from the group consisting oforganometallic compounds, silicon compounds, phosphorous compounds,boron salts, antimony compounds, magnesium salts, coke, and mixturesthereof, on said aluminosilicate; simultaneously forming a methylatingagent from a combination selected from the group consisting of: CO andH₂, CO₂ and H₂, and CO, CO₂ and H₂; and reacting an aromatic compoundselected from the group consisting of toluene, benzene and mixturesthereof with the methylating agent in the presence of the catalyticreaction system to produce a xylene fraction having a PX concentration;and recovering PX where greater than 15% of the aromatic compound isconverted to a xylene fraction and where the PX concentration recoveredin the xylene fraction is greater than 48%.
 47. The method of claim 46where the deposited compounds are converted into oxides.
 48. A methodfor forming para-xylene (PX) comprising simultaneously forming amethylating agent from a combination selected from the group consistingof: CO and H₂, CO₂ and H₂, and CO, CO₂ and H₂; and reacting a feedincluding an aromatic compound selected from the group consisting oftoluene, benzene and mixtures thereof with the methylating agent in thepresence of a catalytic reaction system which converts at least 10% ofthe aromatic compound to a mixture of xylenes, where PX comprises atleast 48% of the mixture of xylenes, and where the catalytic reactionsystem comprises: a first component selected from the group consistingof metals and metal oxides, where the metal element is selected from thegroup consisting of the Groups 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, and 16 of the Periodic Table of Elements (new IUPACnotation); and a second component that is a para-alkyl selectivatedcrystalline aluminosilicate prepared by depositing compounds selectedfrom the group consisting of organometallic compounds, siliconcompounds, phosphorous compounds, boron salts, antimony compounds,magnesium salts, coke, and mixtures thereof, on said aluminosilicate.49. The method of claim 48 where the deposited compounds are convertedinto oxides.